Process and equipment for heat treatment of the body of a preform or of an intermediate-stage container made of a thermoplastic material

Abstract

The invention relates to the thermal treatment of the body of a preform (1) or of an intermediate container made of a thermoplastic material during a process for manufacture of the container, such as a flask or bottle, in particular by blowing or stretching-blowing, the entirety of the body of the preform being heated to a temperature greater than the softening temperature of the material, at least one longitudinal portion (13) of the body (2) of the preform in rotation on itself being heated to a temperature greater than that of the rest (14) of the body, thereby making it possible to produce a finished container incorporating a body having a complex shape.

We claim: 
     
       1. A process for the thermal treatment of the body of a preform or of an intermediate container made of a thermoplastic material during manufacture of a container by blowing or stretching-blowing, during which thermal treatment the preform rotates on a longitudinal axis thereof and travels through an oven wherein the entirety of the preform body is heated to a temperature greater than the softening temperature of the material, the improvement comprising the steps of; a) passing at least one part of the length of the preform body in alternating fashion in front of heating zones and non- or reduced-heating zones disposed on at least one side of a path followed in the oven by the preform, so that at least one longitudinal portion of the preform body, or a plurality of longitudinal portions circumferentially separated from each other, extending over at least said one part of the length of the body is preferentially heated to a temperature greater than that of remaining portions of the body, and   b) spacing the heating zones based on the number of longitudinal portions of the preform body to be preferentially heated and on a perimeter of the preform body, so that the longitudinal portions of the preform body to be preferentially heated are positioned in front of successive heating zones during the combined travel and rotation of the preform, while interposed longitudinal portions to be heated to a lesser degree are positioned in front of successive non- or reduced-healing zones, whereby one or a plurality of relatively hotter longitudinal portions are produced in the body of the preform or of the intermediate container, these portions alternating with relatively cooler interposed longitudinal portions and being capable of being reshaped more easily than said cooler longitudinal potions during subsequent reshaping of the preform body, thereby making it possible to manufacture containers having a body of complex shape and having at all points an approximately uniform wall thickness.   
     
     
       2. A process according to claim 1, wherein the rate of travel of the perform and the speed of rotation of the preform are approximately constant, and wherein the heating zones are spaced apart by substantially uniform distance. 
     
     
       3. A process according to claim 1 or 2, wherein, from at least one side of the oven, the perform bodies are heated discontinuously by successive heating zones spaced apart from each other along the path of travel of the preform. 
     
     
       4. A process according to claim 3, wherein a plurality of successive heating devices spaced apart from each other along the path of travel of the preform are disposed on at least one side of the oven. 
     
     
       5. A process according to claim 4, wherein continuous heating devices are disposed on at least one side of the oven, and successive shields spaced apart from each other along the course of travel of the perform are disposed in front of said heating devices. 
     
     
       6. A process according to claim 1, wherein the body of the preform is heated from one side of the oven and wherein, on the opposite side, thermal radiation is reflected back into successive reflecting zones spaced apart from each other along the path of travel of the perform. 
     
     
       7. A process according to claim 6, wherein a plurality of successive reflectors spaced apart along the path of travel of the perform are disposed on said opposite side of the oven. 
     
     
       8. A process according to claim 6, wherein a substantially continuous reflector is disposed on said opposite side of the oven, and successive, non-reflecting screens spaced apart along the path of travel are disposed in front of said reflector. 
     
     
       9. A process according to claim 6, wherein a substantially continuous, non-reflecting wall is disposed on said opposite side of the oven, and successive reflectors spaced apart along the path of travel are disposed in front of said wall. 
     
     
       10. A process according to claim 1, wherein at least one annular portion of the preform body or intermediate container, or a plurality of annular portions spaced apart longitudinally are heated to a temperature lower than that of the rest of the body, thereby forming in the preform body or the intermediate container one or a plurality of relatively cooler annular portions which alternate with relatively hotter annular portions and that are more difficult to reshape during a subsequent reshaping of the preform body, thereby making it possible to manufacture containers having a body which incorporates a peripheral reinforcement area of increased thickness. 
     
     
       11. A process according to claim 10, wherein the preform body is heated from one side of the oven and wherein, on the opposite side of the oven, thermal radiation is not reflected back in at least one non-reflecting, band-shaped area extending substantially parallel to the direction of the preform travel and located opposite at least one annular portion of the preform body to be heated to a relatively lesser degree, while thermal radiation is reflected back in at least one reflecting band-shaped area extending substantially parallel to the direction of travel of the preform and located opposite a remaining portion of the preform which is to be heated to a relatively greater degree. 
     
     
       12. A process according to claims 8 or 9 wherein the non-reflecting screens or wall absorb incident thermal radiation. 
     
     
       13. An oven for the heat treatment of the body of a preform or of an intermediate container made of a thermoplastic material during a process for manufacture of a container by a blowing or stretching-blowing process, wherein said oven is configured to heat the entirety of the preform body to a temperature greater than the material-softening temperature, the improvement comprising: on at least one side of a path of travel of the preform through the oven while it rotates on a longitudinal axis thereof, an alternating arrangement of heating zones and non- or reduced-heating zones disposed opposite at least one part of a length of the preform body for preferentially heating at least one longitudinal portion of the preform body or several longitudinal portions thereof separated from each other circumferentially and extending over at least said one part of the length of said body to a temperature greater than that of remaining portions of the preform body, wherein the spacing of the heating zones is based on the number of longitudinal portions of the preform body to be preferentially heated and on a perimeter of the preform body such that the longitudinal portions of the preform body to be preferentially heated are positioned in front of successive heating zones during the travel and rotation of the preform, while interposed longitudinal portions to be heated to a lesser degree are positioned in front of successive non- or reduced-heating zones.   
     
     
       14. An oven according to claim 13, wherein the rate of travel of the preform and the speed of rotation of the preform are approximately constant and, the heating zones are spaced apart by substantially uniform gaps. 
     
     
       15. An oven according to claim 13 or 14, wherein said oven comprises discontinuous heating devices arranged on at least one side of the oven to delimit said successive heating zones spaced apart along the path of travel of the preform. 
     
     
       16. An oven according to claim 15, wherein said discontinuous heating devices comprise several successive heating devices spaced apart along the path of travel of the preform. 
     
     
       17. An oven according to claim 15, wherein said discontinuous heating devices comprise a continuous heating element and successive screens positioned in front of said element and spaced apart along the path of travel of the preform. 
     
     
       18. An oven according to claim 13, wherein said oven comprises, on one of its sides, at least one heating device, and on the opposite side, means for reflecting incident thermal radiation to form successive reflecting areas spaced apart along the path of travel of the preform, which form said heating zones. 
     
     
       19. An oven according to claim 18, wherein said reflecting means comprises a plurality of successive reflectors spaced apart along the path of travel of the preform. 
     
     
       20. An oven according to claim 18, wherein said reflecting means comprises a substantially continuous reflector, and successive non-reflecting screens spaced apart along the path of travel of the preform and disposed in front of said reflector. 
     
     
       21. An oven according to claim 18, wherein said reflecting means comprises, on said opposite side, a substantially continuous, non-reflecting wall, and successive reflectors spaced apart in front of said wall along the path of travel of the perform. 
     
     
       22. An oven according to claim 21, wherein a plurality of reflectors are brought together on at least one plate incorporating successive notches and removably attached in front of said non-reflection wall. 
     
     
       23. An oven according to claim 21 or 22, wherein said non-reflecting wall is cooled. 
     
     
       24. An oven according to claim 21 or 22, wherein said non-reflecting wall comprises a stack of bars having blackened faces directed toward the inside of the oven and through which a cooling fluid circulates. 
     
     
       25. An oven according to claim 13, comprising means for heating at least one annular portion of the preform body to a temperature lower than that of remaining portion of the preform body. 
     
     
       26. An oven according to claim 25, wherein said oven incorporates heating devices on one side of the path followed by the preform, and wherein, on the opposite side, said oven comprises at least one area that is non-reflective for thermal radiation, said non-reflecting area being band-shaped and extending substantially parallel to the path of travel of the preform and being disposed opposite said parallel to the path of travel of the preform and being disposed opposite said at least one annular portion of the preform body to be heated to a relatively lesser degree, and at least one area that is reflective for thermal radiation, said reflecting area being band-shaped and extending substantially parallel to the path of travel of the preform and being disposed opposite said remaining portions of the preform body to be heated to a relatively greater degree. 
     
     
       27. An oven according to claims 20, 21, or 26, wherein said non-reflecting screen areas or walls absorb incident thermal radiation.